Mitchell signed a five-year deal with the Steelers. The team did not disclose financial terms.

Mitchell replaces Ryan Clark as Troy Polamalu's partner in the Steelers secondary. After eight seasons, Clark, a 34-year-old unrestricted free agent, is not expected back with the team. He confirmed as much in his own tweet after Mitchell said he was joining the Steelers.

Mitchell, who turns 27 in June, started 14 of 15 games he played in for the Panthers last season -- his only in Carolina. In his first season as a full-time starter, Mitchell recorded four interceptions, 3.5 sacks, two forced fumbles and 66 tackles. He also broke up eight passes.

The Oakland Raiders took him in the second round of the 2009 draft. He spent four seasons in the silver and black before signing with the Panthers last offseason.

Steelers 2014 free agent tracker (UPDATED)

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The Steelers are making some tough roster decisions for the 2014 season. See which free agents are moving on to other teams and which players are staying in Pittsburgh.